This patent document presents a new multiple access technique for Personal Communication Networks (PCN). Personal communication networks are networks that allow individuals and equipment to exchange information with each other anywhere at anytime through voice, data or video. PCN typically include a number of transceivers, each capable of transmitting and receiving information (voice, data or video) in the form of electromagnetic signals. The transceivers may be fixed or portable, and may be identical or one or more of them may be more complex.
The system must allow the transceivers to access each other to enable the exchange of information. When there are a number of transceivers, multiple access, that is, access by more than one transceiver to another transceiver, must be allowed.
One of the constraints of designing a PCN is that a transceiver, or portable radio unit, must be small in size. The smaller the unit, the better for portability. The small size of the units means only small and light-weight power sources can be used. If the portable is to be used for any length of time, it must therefore consume minimal power.
Also, to allow use of the radio frequency spectrum without obtaining a license in North America, the system must use a spread spectrum and satisfy federal regulations. In part, these regulations impose limits on the power and the frequency spread of the signals exchanged between the transceivers. An object of an aspect of this invention is to satisfy those requirements.
Also, transceivers talk to each other over a fixed bandwidth. Because of the limited availability of the RF spectrum, the system must be bandwidth efficient yet at the same time maintain high quality exchange of information at all times in one of the most hostile channels known in communication. The new multiple access technique proposed here addresses all these issues.
The new access technique has a low Bit Error Probability (BER) as well as a low probability of dropped and blocked calls. This is due to the fact that the access technique is robust against multipath, Doppler shifts, impulse noise and narrowband interference. It has a low cochannel interference and little or no intersymbol interference.
The new access technique can offer up to 38 times the capacity of analog FM. It includes in one aspect wideband orthogonal frequency division multiplexing of the information to be exchanged, and may include slow Frequency Hopping (FH). The technique is implemented using Digital Signal Processors (DSP) replacing conventional analog devices. The system operates with relatively small cells. In other aspects, dynamic channel allocation and voice activation may be used to improve the capacity of the system.
Advantages of the present invention include:
1. It can be used indoors as well as outdoors using the same transceivers. If data is to be exchanged, as opposed to voice, the transceiver preferably contains an estimator to allow pre-distortion and post-distortion of the transmitted signal. PA0 2. The system, as compared with prior art systems omits the clock or carrier recovery, automatic gain control or passband limiter, power amplifier, an equalizer or an interleaver-deinterleaver, and therefore has low complexity. PA0 3. The system offers good speech quality, as well as low probabilities of dropped and blocked calls. It is robust against Doppler and multipath shifts. It is also robust against both impulse noise and narrowband interference. PA0 4. The system is flexible, such that at the expense of increased complexity of the DSP receiver it can be applied over noncontiguous bands. This is accomplished by dividing a 100 MHz (in one of the exemplary embodiments described here) band into several subbands each accommodating an integer number of voice channels. PA0 5. The system offers low frame delay (less than 26.2 ms in the exemplary cellular embodiment described here). The transceiver requires low average transmitted power (of the order of 20 .mu.W in the exemplary cellular embodiment described here) which means power saving as well as enhanced biological safety. PA0 6. The system offers up to a 38 fold increase in capacity over the North American Advanced Mobile Phone System (AMPS) which uses analog frequency modulation.
Operation of the system in accordance with the techniques described in this disclosure may permit compliance with technical requirements for spread spectrum systems.
There is therefore disclosed in one aspect of the invention a method for allowing a number of wireless transceivers to exchange information (data, voice or video) with each other. In the method, a first frame of information is multiplexed over a number of frequency bands at a first transceiver, and the information transmitted to a second transceiver. In a cellular implementation, the second transceiver may be a base station with capacity to exchange information with several other transceivers. The information is received and processed at the second transceiver. The frequency bands are selected to occupy a wideband and are preferably contiguous, with the information being differentially encoded using phase shift keying.
A signal may then be sent from the second transceiver to the first transceiver and de-processed at the first transceiver. In addition, after a preselected time interval, the first transceiver transmits again. During the preselected time interval, the second transceiver may exchange information with another transceiver in a time duplex fashion.
The processing of the signal at the second transceiver ma include estimating the phase differential of the transmitted signal and predistorting the transmitted signal.
The time intervals used by the transceivers may be assigned so that a plurality of time intervals are made available to the first transceiver for each time interval made available to the second transceiver while the first transceiver is transmitting, and for a plurality of time intervals to be made available to the second transceiver for each time interval made available to the first transceiver otherwise. Frequencies may also be borrowed by one base station from an adjacent base station. Thus if one base station has available a first set of frequencies, and another a second set of distinct frequencies, then a portion of the frequencies in the first set may be temporarily re-assigned to the second base station.
In an implementation of the invention for a local area network, each transceiver may be made identical except for its address.
Apparatus for carrying out the method of the invention is also described here. The basic apparatus is a transceiver which will include an encoder for encoding information, a wideband frequency division multiplexer for multiplexing the information onto wideband frequency voice channels, and a local oscillator for upconverting the multiplexed information. The apparatus may include a processor for applying a Fourier transform to the multiplexed information to bring the information into the time domain for transmission.